On the initiation of lightning in thunderclouds.

Area of Science:

• Atmospheric Physics
• High-Energy Physics
• Geophysics

Background:

• The precise mechanisms linking lightning and elementary particle fluxes in thunderclouds remain unclear.
• Thunderstorm Ground Enhancements (TGEs) are particle beams observed in thunderclouds, offering a probe for atmospheric processes.
• Lightning flashes are known to abruptly terminate TGE particle fluxes.

Purpose of the Study:

• To investigate the characteristics of interrelated atmospheric processes using TGEs as a probe.
• To understand the role of particle fluxes and cloud charge dynamics in lightning initiation.
• To determine if Relativistic Runaway Electron Avalanches (RREA) contribute to lightning discharge.

Main Methods:

• Utilizing precise electronics to monitor particle flux dynamics and cloud charge center rearrangements.
• Analyzing the energy spectra of TGEs before and after lightning events.
• Correlating the decline in particle flux with the timing of atmospheric discharges on millisecond timescales.

Main Results:

• Particle flux decline was observed to occur simultaneously with the rearrangement of charge centers within the thundercloud.
• The high-energy portion of the TGE energy spectra disappeared immediately after a lightning flash.
• The decline in particle flux coincided with initial atmospheric discharges on a millisecond timescale.

Conclusions:

• Relativistic Runaway Electron Avalanches (RREA) within thunderclouds assist in the initiation of negative cloud-to-ground lightning.
• RREA can provide sufficient ionization to play a significant role in unleashing lightning flashes.
• The study provides new insights into the interplay between particle physics and atmospheric electrical phenomena in thunderclouds.